The invention pertains to a liquid acquisition layer for an absorbent article such as a sanitary napkin, an incontinence protector, a diaper, a panty-liner, a bed protector or the like, which exhibits a carrier layer against which individual fibres, detached from each other and each exhibiting two fibre ends, are attached with one fibre end against the carrier layer with an attachment angle xcex1 between the carrier layer and each individual fibre. The invention also relates to an absorbent article provided with the liquid acquisition layer.
Great demands are made on both softness and dryness of liquid acquisition layers for absorbent articles of the herein intended type, which are intended to be in contact with the body of the user during use.
However, it has proved to be difficult to achieve a liquid acquisition layer having a soft and textile-like surface which at the same time remains dry during use.
One problem, when using nonwoven materials or other similar textile materials as liquid acquisition layers for absorbent articles, is that the fibre structure of the material absorbs liquid when the cover layer is wetted. A certain quantity of the liquid is not conducted downwards to the underlying absorbent structure, but remains instead in the liquid receiving cover layer. Since the liquid receiving cover layer is in contact directly against the body, such articles are perceived as being wet and uncomfortable to wear already after an initial wetting. Furthermore, the wet surface which is in direct contact with the skin results in an increased risk of skin irritation and infections.
The main reason for part of the liquid remaining in textile cover layers is that such textile materials usually consist of an irregularly shaped fibre structure with fibres or fibre filaments directed along the plane of the material. This implies that excreted body fluid, by means of the capillary action of the fibres, is distributed along the fibre structure in the direction of the plane of the material. Also liquid which is not absorbed by the fibre capillaries is conducted along the fibre structure in the plane of the material and is collected in voids between the fibres, where the liquid remains without being able to be further distributed to materials on the inside. These factors result in a certain amount of the liquid remaining in the cover layer and create a wet surface closest to the user.
Another problem with the present nonwoven materials, having fibres primarily directed along the material plane, is that the possibility to control the wetting course, by utilizing different types of fibres exhibiting differences in properties such as for example wettability, is limited. Furthermore, the possibility to control the wetting course is limited where the location of the fibres and their design are concerned.
Particularly with regard to the sanitary napkins and panty-liners of today, which should be discreet to wear during use, another problem is that such articles, in order to obtain a liquid absorbent structure and at the same time maintain a dry surface closest to the user, are built up from a number of layers exhibiting essentially different properties. This implies that such articles are rather voluminous and therefore often are perceived as being uncomfortable and indiscreet. A further disadvantage with having a number of layers is that the material consumption for these disposable articles is high, which results in a high manufacturing cost and a high usage of raw material.
From U.S. Pat. No. 3,967,623 it is known to use a liquid-pervious cover layer consisting of a perforated plastic layer as a carrier material, on which fibres treated with wetting agent are applied in order to create a soft and fluffy surface. The individual fibres are oriented so that they are directed upwards towards the user during use and are approximately 5 mm long. Since the fibres are directed upwards towards the user, a soft and fluffy surface is created. However, the problem that the liquid transfer from the fibres to the absorbent body on the inside is poor remains to be solved, which results in the surface closest to the user remaining wet after the initial wetting.
BE 09300552 relates to a cover layer for an absorbent article, which cover layer consists of a plastic film, which at least on one side is covered with fibres which are not fused together and which are attached at an angle towards the plastic film. In order to obtain such a structure the fibres may, for example by means of flocking, be attached with one of their fibre ends against a melted fibre fixation layer on the plastic film. The plastic film can be perforated so that the material becomes liquid-pervious. The fibres are between 0.3 and 2.5 mm long and the thickness may vary depending on how soft the layer should be. Different fibres may be used, such as for example viscose, cotton, polyethylene, polypropylene, polyester, and polyamide. The risk of the liquid spreading in the material plane, and consequently along the surface of the cover layer, is minimal with this previously known cover layer. Furthermore, the cover layer exhibits a soft surface closest to the user. However, the problem of achieving a dry surface remains with this previously known cover material, when the layer is used as a liquid-pervious surface material on an absorbent article.
The problems with achieving a liquid acquisition surface, for, for example, liquid-pervious cover layers intended for absorbent articles or for liquid acquisition articles, such as for example a panty-liner, which liquid acquisition surface is soft and exhibits a dry surface also after wetting, have been substantially eliminated by the present invention.
Accordingly, a soft, skin-friendly and textile-like liquid acquisition layer for an absorbent article has been achieved by means of the invention, which layer has an ability to conduct the liquid downwards in the structure and, by means of this, to maintain a dry surface closest to the user.
A liquid acquisition layer according to the invention exhibits a carrier layer against which separate fibres, detached from each other and each exhibiting two fibre ends, are attached with one fibre end against the carrier layer with an attachment angle xcex1 between the carrier layer and each individual fibre. The liquid acquisition layer is primarily characterized in that the individual fibres comprise at least a first fibre type and a second fibre type. Since the fibres are not bonded together into a nonwoven fabric but instead are oriented so that an angle arises between the fibre and an underlying carrier material, accordingly, increased possibilities are obtained to design a cover layer which utilizes the properties of different fibres, for example the liquid-conducting ability of different fibres.
According to a preferred embodiment, the fibres of the first fibre type are longer than the fibres of the second fibre type. Thereby, the fibres of the first fibre type are suitably 0.3-1.5 mm long, while the fibres of the second fibre type are 1.5-5 mm long. The fibre length is dependent on the other properties of the fibres, such as for example their liquid absorption ability. Furthermore, the fibre length is dependent on which type of absorbent article the liquid acquisition layer is intended for, since urine and menstrual fluid are different from each other, among other things with regard to viscosity and surface energy. This implies that the length of the fibres must be adapted to these conditions in order to achieve an optimum liquid acquisition layer with regard to dryness and softness.
According to one embodiment, the longer fibres are more hydrophobic than the shorter fibres. Since the longer fibres which are located closer to the skin of the user during use are more hydrophobic than the shorter fibres, a distance is created between the skin and the shorter liquid-absorbing fibres. Accordingly, the more hydrophillic fibres are constituted by fibres which exhibit a lower contact angle in contact with body fluid than the more hydrophobic fibres. The hydrophillic fibres may, for example, be constituted by cellulose, viscose, polyester or hydrophobic fibres treated with wetting agent, such as for example polyolefin fibres treated with wetting agent. The longer and more hydrophobic fibres are for example constituted by untreated polyolefin fibres. The advantage with this embodiment is that the surface closest to the body is kept dry also when repeated wettings occur, and the risk of the liquid spreading along the plane of the liquid acquisition layer is nearly eliminated.
According to another embodiment, a difference is obtained in the liquid absorption ability of the fibre types by means of the shorter fibres exhibiting finer capillaries, i.e. a smaller pore radius than the longer fibres. Accordingly, a liquid gradient from regions with longer fibres having larger capillaries to the shorter fibres having finer capillaries is created. Thereby, the liquid is mainly absorbed in regions with shorter fibres, which implies that the surface closest to the user remains dry. An advantage with this embodiment is that both fibre types can be constituted by the same material, whereby the difference in liquid absorption ability is obtained by means of the fibre types exhibiting differences in pore radius. Still another possibility to control the liquid absorption/liquid conducting ability of the fibre regions is achieved by means of the regions with the shorter fibres exhibiting a higher fibre density than the regions with the longer fibres. As a result of this, fine external cavities, i.e. external capillaries, are created in the regions with the shorter fibres, something which results in a higher liquid absorption/liquid conducting ability between the fibres in these regions.
According to another embodiment, the two fibre types exhibit different geometry. For instance, the second fibre type is constituted by fibres having a branched cross-section, such as the fibres described in WO 93/01779. Since the fibres exhibit a branched cross-section, cavities are created, i.e. external capillaries between the fibres, resulting in an increased liquid absorption ability.
The second fibre type may further be constituted by fibres which collapse, i.e. shrink, when they are wetted. When wetting of such a liquid acquisition surface occurs, the distance between the user and the liquid-absorbing fibres is improved. The geometrical construction of the fibres may of course adopt other shapes, resulting in an increased distance between the user and the liquid-absorbing fibres and/or improving the liquid absorption/liquid conducting ability of the second fibre type. The first fibre type is preferably constituted by fibres which are hydrophobic, such as for example polyolefin fibres, or other fibres suitable for the purpose.
According to still another embodiment, the fibre types exhibit a difference in stiffness. Since the first fibre type having longer fibres exhibits a lower stiffness than the second fibre type, a soft surface is created against the user at the same time as the stiffer and shorter fibre provides the liquid acquisition layer with stability. Accordingly, the risk of the article being creased during use is minimized. This implies that the article is more comfortable to wear, and the risk of the body fluid leaking out to the panties of the user because of creasing of the article is nearly eliminated.
According to one embodiment, the angle xcex1 between the carrier layer and each individual fibre is between 30-90xc2x0.
According to one embodiment, the angle xcex1 between the carrier layer and each individual fibre is approximately 90xc2x0, but may of course vary slightly between the different fibres. The advantage with such an embodiment is that the body fluid rapidly is conducted in a direction straight downwards into the absorbent structure and, accordingly, the risk of the article being perceived as wet is minimized.
According to another embodiment, the angle xcex1 between the carrier layer and each individual fibre is between 30-70xc2x0.
By means of this embodiment, the surface maintains a clean and dry visual appearance also after use, since the shorter wet fibres are not visible when the user observes the sanitary napkin from above.
According to one embodiment, the cover layer exhibits a regularly alternating pattern comprising portions of fibres of the first fibre type and portions of fibres of the second fibre type. Since the cover layer thus comprises regions with fibres of different length, where the longer fibres create raised barriers, a distance is created between the skin and the liquid-absorbing fibres. Furthermore, liquid is prevented from spreading across the surface of the cover layer which is in direct contact against the user during use. The alternating pattern may be arranged in rows, checks, or in another pattern advantageous for the manufacture and use. Furthermore, the proportion of long fibres in relation to the proportion of short fibres may vary across the surface of the cover layer, as may the fibre density and the dimension of the alternating pattern. Factors which affect the selection of the above-mentioned pattern structure are the properties of the fibre types, such as for example their liquid absorption ability. The properties of the carrier material are also of importance. Furthermore, it is of essential significance which type of liquid the article is intended to absorb. As earlier mentioned, urine and menstrual fluid exhibit differences, for example with regard to viscosity and surface energy. A liquid-pervious cover layer for different types of articles exhibiting a reduced surface wetness and an increased softness may accordingly be obtained by means of the possibility to vary the pattern structure.
Since the article rapidly is saturated with liquid within the region around the wetting site, i.e. within the region of the crotch portion of the article which the body fluid reaches first, the carrier layer of the cover layer, according to a preferred embodiment, exhibits a regularly alternating pattern exhibiting separated regions of fibres of the first fibre type and a substantially continuous region of fibres of the second fibre type. The continuous region with liquid-absorbing fibres facilitates the transport of the liquid from the wetting zone to the remaining parts of the liquid acquisition layer of the article. Accordingly, the risk that the liquid acquisition layer is saturated with liquid within the wetting zone, with accompanying risk of leakage, is eliminated.
According to another embodiment, the cover layer exhibits continuous regions of the different fibre types, for example in a row pattern along the longitudinal direction of the article. Also in this embodiment, the advantage is that the liquid can be distributed out towards the end portions of the article and the risk of the area around the wetting site being saturated with liquid, with leakage as a consequence, is thus eliminated.
According to another embodiment, the entire carrier layer of the cover layer comprises both fibres of the first fibre type and fibres of the second fibre type, which are uniformly distributed across the entire surface of the carrier layer. In this way a material is achieved which across the entire surface has short and long fibres, respectively. An advantage with such an embodiment is that the cover layer is easy to manufacture, since no synchronization problems will arise. A further advantage with such an embodiment is that the cover layer looks dry even during use, since the short and liquid-absorbing fibres are hidden by the longer and more hydrophobic fibres.
A further embodiment comprises a cover layer exhibiting separated regions of the first fibre type and separated regions of the second fibre type. This embodiment may be advantageous when the risk of the liquid remaining in the cover layer already is eliminated, for example when an underlying absorbent structure effectively drains the cover layer of liquid. Another advantage with such an embodiment is that the liquid distribution in the cover layer is reduced.
Furthermore, the invention includes an absorbent article such as a sanitary napkin, a panty-liner, a diaper, or the like comprising an absorbent body enclosed in a cover wherein at least a portion of the cover consists of a liquid-pervious cover layer. The liquid-pervious cover layer comprises a carrier layer against which individual fibres, detached from each other and each exhibiting two fibre ends, are attached with one fibre end against the carrier layer. Between the cover layer and each individual fibre an attachment angle arises. The individual fibres comprise at least a first fibre type and a second fibre type, where the fibres of the first fibre type are longer than the fibres of the second fibre type. Furthermore, the fibres of the first fibre type are more hydrophobic that the fibres of the second fibre type.
According to still another embodiment, the liquid-pervious cover layer of the article is designed so that the cover layer within the crotch region primarily exhibits fibres of the first fibre type. Accordingly, the liquid-pervious cover layer primarily exhibits short, hydrophillic fibres within the crotch region, while the cover layer in the two end portions primarily exhibits long, hydrophobic fibres. By means of this, a cover layer is obtained which only exhibits a wet region within the crotch region of the article during use.
According to a similar embodiment of the article, the liquid-pervious cover layer is designed so that the central portion of the crotch region at least substantially comprises fibres of the second fibre type and that the two edge portions of the crotch region at least substantially comprise fibres of the first fibre type. Furthermore, the cover layer within the two end portions primarily comprises fibres of the first fibre type. The embodiment is similar to the preceding one, but since the liquid-pervious cover layer along the entire edge portion of the article comprises fibres which are longer and more hydrophobic than the fibres in the central portion of the crotch region, this implies that the risk of the liquid spreading out on the side edges of the article and leaking further to the pants of the user is nearly eliminated.
Still another embodiment is constituted by a panty-liner or a similar absorbent article, where only a minor absorption capacity is necessary. According to this embodiment, the carrier layer in the liquid acquisition layer is liquid-impervious and, accordingly, constitutes the backing material of the article. According to the invention, individual fibres detached from each other are attached in one of the two ends of the fibre, with an attachment angle between the carrier layer and each individual fibre, against the side of the liquid-impervious carrier layer which is intended to be in contact with the user during use. The individual fibres at least comprise a first fibre type and a second fibre type, where the fibres of the first fibre type are longer than the fibres of the second fibre type. Furthermore, the shorter fibres are liquid-absorbing while the longer fibres not are liquid-absorbing. Regions with the longer fibres serve as raised barriers between the user and the shorter liquid-absorbing fibres during use. An advantage with this embodiment is that the shorter fibres in the cover layer have an ability to absorb liquid, which implies that no further absorbent structure is necessary. Accordingly, the material consumption for these articles is reduced, which results in a lower manufacturing cost and a lower raw material use. Still another advantage with such articles is that they are thinner and thus more comfortable and more discreet to wear.
In the following, the invention will be described in greater detail with reference to the figures shown in the attached drawings, wherein
FIG. 1 shows a cross-section through a liquid acquisition layer according to the invention,
FIG. 2 shows a sanitary napkin with a cover layer according to the invention, seen from the side which is intended to be facing towards the user during use,
FIG. 3 shows another sanitary napkin according to the invention, seen from the side which is intended to be facing towards the user during use,
FIG. 4 shows another cross-section through a liquid acquisition layer according to the invention, and
FIG. 5 shows another cross-section through a liquid acquisition layer according to the invention.